Swirl anti-ice system

ABSTRACT

A system for circulating heated gases within the circular leading edge of a jet engine housing to prevent ice build-up thereon, or to remove accumulated ice thereform. Hot gases such as air from a hot, high pressure section of the jet-engine are directed through a conduit. The conduit enters the annular leading edge housing, usually from the aft side through a bulkhead, then turns about 90° to a direction tangential to the leading edge annulus. The hot gases exiting the tube entrain the cooler air in the housing, causing a much larger mass of air to swirl circularly around the annular housing. The entering hot gasses heat the mass of air to an intermediate, but still relatively hot, temperature. This large mass of circularly moving hot air is quite efficient in uniformly transferring heat to the skin of the leading edge without leaving any relatively cold areas and preventing the formation of ice thereon.

BACKGROUND OF THE INVENTION

The formation of ice on aircraft wings, propellers, engine inlets, etc.has been a problem since the earliest days of heavier-than-air flight.Any accumulated ice adds considerable weight, and changes the airfoil orinlet configuration making the aircraft much more difficult to fly andin some cases has caused the loss of aircraft. In the case of jetaircraft, chunks of ice breaking loose from the leading edge of anengine inlet housing can severely damage turbine blades or otherinternal engine components and cause engine failure.

Many attempts have been made to overcome the problems and dangers ofaircraft icing. For example, proposals have been made, as described inU.S. Pat. No. 2,135,119 to mechanically vibrate external surfaces tobreak ice loose, or, as described in U.S. Pat. No. 3,549,964 to generateelectromagnetic pulses in the aircraft skin to break ice loose. Thesesystems, however, tend to be heavy and complex and to only removeexisting ice, rather than prevent ice formation.

Heating areas of the aircraft prone to icing has been suggested manytimes. The heating ranges from microwave heating as suggested by U.S.Pat. No. 4,060,212 to feeding hot gases through holes in the skin, assuggested by U.S. Pat. No. 4,406,431, to resistance heating of thesurfaces (U.S. Pat. No. 1,819,497) to actually burning fuel adjacent toice-prone surfaces, as described in U.S. Pat. No. 2,680,345. While eachof these methods have some advantages, none has been truly effective.

One of the most common anti-ice techniques has been the ducting of hotgases into a housing adjacent to the likely icing area. Typical of thepatents describing such hot gas techniques are U.S. Pat. Nos. 3,057,154;3,925,979; 3,933,327 and 4,240,250. In each case, the hot gas conduitssimply dump hot gases into a housing, such as the leading edge of a jetengine housing or a wing leading edge. While often useful, these systemsare not fully effective due to the low quantity of hot gases introducedrelative to the mass of air in the housing, the heating effect tendingto be limited to the region near the hot gas introduction point, and thecomplexity of the hot gas duct system.

Thus, there is a continuing need for improving aircraft icing preventionand removal systems having greater efficiency and mechanical simplicity.

SUMMARY OF THE INVENTION

The above-noted problems, and others, are overcome by the anti-icesystem of this invention, which basically comprises at least one conduitmeans or tube to direct hot gas, such as air, from a source of hot, highpressure gases such as a hot, high pressure region of a jet engine to anannular housing around the leading edge of the engine housing. The hotgas conduit enters the housing, generally through a transverse bulkheadfrom the back, then s immediately bent about 90° so as to expel the hotgases at high velocity substantially along a tangent to the annularhousing interior. Preferably, the outlet end of the hot gas conduitincludes at least one nozzle configured to optimize the velocity of theexisting hot gases.

As the exiting hot air begin to mix with the larger mass of stationaryair in the housing, heat is transferred bringing the mass of air up toan intermediate, but still high, temperature. At the same time, thesmall stream of high speed gases begin to entrain the larger air mass,bringing the velocity of gases and air to an intermediate velocity. Inessence, energy is conserved by trading high velocity and hightemperature in a small mass of gases for lower velocity and slightlylower temperature in a larger mass of air/gas mixture.

This has been found to be a very efficient and simple anti-icing systemin that effective heat transfer takes place from the large mass ofheated moving air to the housing walls while retaining mechanicalsimplicity. There are no moving mechanical parts or electrical parts tojam or burn-out.

BRIEF DESCRIPTION OF THE DRAWING

Details of the invention, and of preferred embodiments thereof, will befurther understood upon reference to the drawing, wherein:

FIG. 1 is a schematic elevation view, partially in section of aconventional gas turbine or jet engine showing the system of thisinvention;

FIG. 2 is a schematic perspective view of the annular engine inletleading edge housing with the skin removed;

FIG. 3 is a schematic perspective view of details of the annular inletleading edge showing my novel hot gas nozzle;

FIG. 4 is a schematic perspective detail view showing an ejectorembodiment of my hot gas nozzle;

FIG. 5 is a schematic perspective detail view showing a multi-nozzleembodiment of my hot gas nozzle;

FIG. 6 is a schematic perspective detail view showing aconverging-diverging embodiment of my hot gas nozzle; and

FIG. 7 is a schematic perspective detail view showing a piccolo-tubeembodiment of my hot gas nozzle.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 1, there is seen a schematic representation of ajet engine 10 of the sort suitable for aircraft propulsion. The turbineis housed within central housing 12. Air enters through inlet section14, between nose cap 16 and the annular housing 18 which constitutes theforwardmost section of the engine nacelle 20. Engine thrust is producedby burning incoming air and fuel within central housing 12. Hot, highpressure propulsion gases pass through exhaust assembly 15 and out therear of the engine.

In flight, under "icing conditions", ice tends to form on annularhousing 18 and nose cap 16 (in addition to other aircraft components notbeing considered here). The ice changes the geometry of the inlet areabetween annular housing 18 and nose cap 16, adversely affecting therequired quantity and flow path of incoming air. Also, pieces of ice mayperiodically break free from these components and enter the engine,damaging rotor blades and other internal engine components. Thisinvention is concerned with preventing accumulation of ice on thesurface of annular housing 18. Other techniques may be used with nosecap 16 and other aircraft parts, such as wing leading edges, controlsurfaces or the like.

Within compressor section 17 there is a region containing hot, highpressure gases. A conduit means or tube 22 is connected at a first end24 to that hot, high pressure region. The other end 26 of tube 22penetrates a bulkhead 28 at the back of annular housing 18. In someprior art ice prevention methods, the tube simply terminates at thispoint, serving to deliver hot gases into the annular space. Even withcomplex, heavy, ducting within the annular housing, heating was notuniform, with some hot spots and other cold spots which tended toaccumulate ice. Sometimes a large number of tubes 22 were used in orderto bring more hot air forward. The additional tubes added considerableweight and still allowed hot and cold areas.

Conduit means 22 could have a configuration other than the preferredtube, if desired. For example, a channel could be formed along the outersurface of the engine housing. Also, the hot gases could be produced inany conventional heater, rather than the preferred hot engine section,if desired. An auxiliary source of hot gases could be provided for usein melting ice when the aircraft is on the ground and the engine is notoperating.

FIG. 2 shows the annular housing 18 in perspective with the sheetaluminum skin removed to show the internal structure. Between rearbulkhead 28 and the skin are two metal rings 31 and 32. Several metalsupport straps 34 extend between rings 31 and 32 and to maintain theskin in the desired shape. A plurality of holes 36 are provided inbulkhead 28 to allow gases within the annular housing 18 to escape. Thefront end 26 of tube 22 is seen penetrating through bulkhead 28.

The primary novel feature of my invention is most clearly shown in FIG.3. After front end 26 of tube 22 penetrates bulkhead 28 and entersannular housing 18, it is Cm most embodiments) bent substantially 90° sothat the very end 30 of tube 22 is tangent to the centerline of annularhousing 18. This seemingly simple change makes a surprising improvementin the de-icing capability of the system. As hot high-pressure gasesexit very 30 of tube 22, the high velocity flow entrains air withinhousing 18 and causes it to swirl around the circular interior. The hotgases rapidly mix with the stagnant air, causing the entire air mass tomove in the circular direction and to reach a temperature intermediatebetween the entering hot gas temperature and that of the stagnant air.The temperature within housing 18 rises until a stable temperature isreached at which heat lost be conduction through the skin of housing 18and carried off with exhaust gases through holes 36 equals the heatbeing brought in by additional hot gases through tube 22. This heattransfer is sufficient to prevent the formation of ice on the exteriorof housing 18. In only the most extreme conditions will it be desirableto add second tube 22 to increase hot gas flow. Because of the swirlingeffect and the constant mixing of the incoming hot gases with gases inthe housing there will be no hot or cold spots. The temperatureimmediately downstream of tube end 30 will be only very slightly higherthan that just upstream of that hot gas inlet because of the continuousmovement of the gas mass within housing 18.

In a typical aircraft engine, the volume of annular housing 18 may beabout 10 ft.³. With such an engine, tube 22 may have a diameter of about1.5 in. and should carry hot gasses having a temperature of about 100°to 500° F. and a gas velocity of about 3 to 30 ft/min. Under theseconditions the temperature within annular housing 18 can be maintainedat a temperature of from about 35° to 41° F. when outside airtemperature is about -40° F.

Preferably the mass flow rate of gases and air moving in the annular ofthe housing 18 is at least about three times the mass flow rate of gasesleaving the tube end 30.

End 30 of tube 22 may have any suitable configuration. Examples areshown in FIGS. 4-7. Aerodynamic fairings may be used on the tubes or thetubes may be configures into aerodynamic shapes to increase performance.In many cases, a simple cylindrical end corresponding to the diameter oftube 22 may be sufficient. In other cases, hot gas velocity may beincreased, if desired, by providing a converging diverging nozzle on end30 corresponding to a garden hose nozzle or the like.

The number and size of outlet holes 36 will be selected to allow aquantity of gases to exit housing 18 corresponding to the quantityentering through tube 22. Smaller holes 36 will result in undesirablehigher pressure in housing 18 while larger (or more in number) holes 36will reduce that pressure. Holes 36 may have any suitable number orshape. Preferably, holes 36 lie in a plane parallel to the direction ofgas flow within the annular housing to avoid direct impingement of therapidly moving gases on the holes.

FIGS. 4-7 illustrate several preferred embodiments of my hot gas nozzle.Excellent performance is obtained with the ejector nozzle as seen inFIG. 4. Tube 26 penetrates bulkhead 28 and is bent about 90° in thedirection of desired annular gas flow. The end of tube 26 has aconverging nozzle 50. A sleeve 52 surrounds nozzle 50 and is held inplace by several webs 54. The interior surface of sleeve 52 has aconverging-diverging shape 56 to provide the desired venturi effect.

If desired a plurality of spaced tubes 58 may extend from a manifold(not shown) behind bulkhead 28 connected to tube 26. Each of tubes 58may extend a different distance beyond bulkhead 28 before making theabout 90° turn, and may lie in one or several horizontal planes. Theends of tubes 58 may be plain or may have any desired nozzleconfiguration, such as those shown in FIGS. 4 and 6. While the tube bendis preferrably about 90°, the angle may also be varied as desired for aparticular application.

Hot gas velocity may be increased as seen in FIG. 6 by using aconverging-diverging nozzle 60 at the end of tube 26, which has enteredthrough bulkhead 28 and been bent about 90°.

As seen in FIG. 7, a straight tube 62 with a closed end 64 could enterthrough bulkhead 28 and have a plurality of holes 66 in the direction ofdesired hot gas flow. This "piccolo" tube can be bent slightly in anydesired direction and two or more space piccolo tubes may be used, ifdesired. The tube 62 may have an airfoil shape to reduce drag on themoving mass of gas in the annular housing.

While the nozzle types and arrangements shown in FIGS. 4-7 are preferredfor most effective performance, any other type of tube or nozzle may beused. The preferred nozzles as shown may be used in any suitable numbersand arrangements.

While certain specific assemblies, structural arrangements and sizes areprovided in the above description of preferred embodiments, these may bevaried where suitable with similar results. For example, the size and/ornumber of tubes 22 and the temperature and velocity or pressure of thehot gases directed to annular housing 18 may be selected in accordancewith the icing conditions anticipated to be encountered by the specificaircraft.

Other applications, variations and ramifications of this invention willoccur to those skilled in the art upon reading this disclosure. Thoseare intended to be included within the scope of this invention asdefined in the appended claims:

What is claimed is:
 1. An anti-icing system for .Iadd.a nose cowl for an .Iaddend.annular .Iadd.inlet of an aircraft .Iaddend.jet engine . .housing.!. .Iadd.propulsion system for an aircraft .Iaddend.which comprises:a source of high pressure hot gas; at least one conduit means to carry hot gases from said source; a substantially closed annular . .housing.!. .Iadd.single skin nose cowl having an exterior surface and an interior surface and positioned .Iaddend.at the leading edge of .Iadd.an inlet .Iaddend.of a jet engine .Iadd.propulsion system and arranged for grazing flow of ambient air over the outer exterior surface when the aircraft is in flight.Iaddend., the annular . .housing.!. .Iadd.nose cowl .Iaddend.containing a quantity of air; said at least one conduit means extending into said . .housing.!. .Iadd.nose cowl.Iaddend.; an outlet on the end of each of said at least one conduit means extending into said . .housing.!. .Iadd.nose cowl.Iaddend., said outlet oriented to eject said hot gases at high velocity substantially tangential to a centerline of said annular . .housing.!. .Iadd.nose cowl.Iaddend.; the mass flow rate of the gases and air swirling in said annular . .housing.!. .Iadd.nose cowl in a rotational direction around the interior of said annular nose cowl and in direct contact with the interior surface of such nose .Iaddend.being at least about three times the mass flow rate of gases leaving said outlet; and whereby the high velocity hot gases entrain .Iadd.said quantity of .Iaddend.air within said annular . .housing.!. .Iadd.nose cowl .Iaddend.so that the total volume of air and gases swirling around .Iadd.the interior of .Iaddend.said annular . .housing.!. .Iadd.nose cowl .Iaddend.has a substantially uniform temperature intermediate between that of said air and said hot gases .Iadd.and by direct contact with the interior surface of the nose cowl substantially uniformly heating the nose cowl to a temperature that is sufficiently high to preclude the formation of ice on the exterior surface of the nose cowl by the grazing flow of ambient air when the aircraft is in flight.Iaddend..
 2. The system according to claim 1 wherein the aft end of said annular . .housing.!. .Iadd.nose cowl .Iaddend.is closed by a transverse bulkhead having at least one hole to allow air and gases with said . .housing.!. .Iadd.nose cowl .Iaddend.to escape.
 3. The system according to claim 2 wherein said conduit means enters through said bulkhead and is bent about 90° to said tangential orientation.
 4. The system according to claim 1 wherein said outlet includes a nozzle means to increase the velocity of exiting gases.
 5. The system according to claim 1 wherein the source of said hot gases is a hot, high pressure region of said jet engine.
 6. The system according to claim 1 wherein said outlet means comprises a converging nozzle extending in the direction of desired gas flow in said . .housing.!. .Iadd.nose cowl .Iaddend.and a converging-diverging sleeve surround and spaced from said nozzle.
 7. The system according to claim 1 wherein said outlet means includes a plurality of tubes ending in spaced hot gas outlets extending in the direction of desired gas flow within said . .housing.!. .Iadd.nose cowl.Iaddend..
 8. The system according to claim 1 wherein said outlet means comprises at least one tube extending in the direction of desired gas flow in said annulus and having a converging-diverging nozzle at the tube end.
 9. The system according to claim 1 wherein said outlet means comprises at least one piccolo tube extending into said housing substantially transverse to the direction of desired gas flow in said . .housing.!. .Iadd.nose cowl .Iaddend.substantially transverse to the direction of desired gas flow in said . .housing.!. .Iadd.nose cowl.Iaddend., said tube having a plurality of holes along the side thereof in said direction of desired gas flow.
 10. An anti-icing system for annular jet engine housings which comprises:a hot, high pressure region of a jet engine; at least one conduit means adapted to carry hot gases from said region having a temperature of about 100 to 500 degrees F. and a velocity of about 3 to 30 ft./min.; a substantially annular .Iadd.single skin .Iaddend.housing .Iadd.having an exterior surface and an interior surface and positioned .Iaddend.at the leading edge of said engine, a bulkhead closing the aft end of said .Iadd.single skin .Iaddend.housing .Iadd.and .Iaddend.having at least one hole to allow air and gases within said housing to escape; said at least one conduit extending into said housing through said bulkhead; at least one outlet at the end of each conduit within said housing, said at least one outlet oriented to eject said hot gases at high velocity substantially tangential to a centerline of said annular .Iadd.single skin .Iaddend.housing; nozzle means connected to said at least one outlet for increasing the velocity of gases exiting therefrom; and the high velocity hot gases entraining air within said annular .Iadd.single skin .Iaddend.housing so that the total volume of air and gases swirling around .Iadd.the interior of .Iaddend.said annular housing .Iadd.in a rotational direction .Iaddend.has a substantially uniform temperature of from about 35 to 41 degrees F. when the outside air temperature is about -40 degrees F., and the mass flow rate of said gas and air is at least about three times the mass flow rate of the gases leaving said outlet .Iadd.whereby such rotating hot gases and air by direct contact with the interior surface of single skin annular housing raise the temperature of said housing to a substantially uniform temperature that is sufficiently high to preclude the formation of ice on the exterior surface of said housing.Iaddend.. 